Lubricant



Patented Jan. 16, 1945 UNITED STATES PATENT OFFICE LUBRICANT No Drawing. Application December 4, 1940, Serial No. 368,504

9 Claims.

This invention relates to lubricants for use under high pressure conditions, and particularly to an extreme pressure lubricant suitable for use in hypoid gears and in extreme pressure industrial lubrication.

It has previously been proposed to utilize sulphurized lubricants containing lead soaps for lubrication under high pressure conditions. However, these prior lubricants were not sulficiently resistant to heating and oxidation so that they thickened upon continued use at elevated temperatures, and some of the prior lubricants would not carry a sufficiently high load. It is an object of this invention to povide an extreme pressure lubricant of high load-carrying capacity I which is resistant to thickening and other objectionable changes, especially at elevated temperatures of the order of 300 to 350 F.

It has been found that an extreme pressure lubricant, of marked improvement over those extreme pressure lubricants heretofore known, can be prepared from a sulphurized mineral oil, lead naphthenate, and an active extreme pressure base, such as tricresyl phosphate.

In the preparation of the improved lubricant, a mineral oil is sulphurized by heating with free sulphur, in the absence of added fatty oil or other constituents highly reactive with sulphur, at a temperature of about 400-425 F., and preferably about 400-410" F. for a controlled .period of time. The quantity of sulphur employed is calculated to give about 0.5-1.0% of active combined sulphur in the mineral oil, such that it is in a condition to provide maximum extreme pressure characteristics, but is only slightly corrosive toward copper, i. e., it darkens a copper strip only slightly when the copper strip is heated in the oil at 212 F. for one hour. This copper strip test serves as a means of controlling the sulphurizing process. In order to provide the above proportion of active combined sulphur in the mineraloil, about 1.5-2.0% by weight of sulphur is generally added, the excess of sulphur passing 01f as vaporous decomposition products during the sulphurizing treatment, or being otherwise removed as sediment from the sulphurized mineral oil. After the mixture of sulphur and oil has been heated for about four hours at about 400 F., it is tested by the copper strip test, and if it is found to be too corrosive, it is heated for a longer period of time. Ordinarily, a period of heating of from four to eight hours is sufiicient. Further heating past the stage at which the oil is only slightly corrosive to copper is unnecessary and may thicken the oil excessively.

The mineral oil to be sulphurized is a lubricating oil, either a residual oil or a blend of residual and distillate oils of such viscosity as to give the desired characteristics in the resulting gear lubricant. For example, paraffin base lubricating oils from Oklahoma crude, having a Saybolt Universal viscosity of 180 to 300 seconds at 210 F. may be used. Such lubricating oils may be blended with lighter distillate oils of paraflin or naphthene base, such as a naphthene base lubricating oil having a Saybolt Universal viscosity of about 200 seconds at F., designated as 200 Pale Oil, in order to obtain products of different viscosities. It is preferable to sulphurize a blend of light distillate and heavy residual oil to give the desired viscosity rather than to sulphurize the oils separately. Sulphurization of 200 Pale Oil produces considerable oil-insoluble sludge and vaporization losses are high, but these difficulties are largely obviated by sulphurizing a blend of 200 Pale Oil and the desired heavy residual oil. No difliculty is experienced in sulphurizing the heavier oils separately. For the heaviest grades of extreme pressure lubricant, a mineral oil residuum having a Saybolt Universal viscosity of about 700 seconds at 210 F. may be blended with a lubricating oil having a Saybolt Universal viscosity of about 190 seconds at 210 F.

The sulphurized mineral oil is rendered substantially non-corrosive to the copper strip test by the addition of a small amount of a fatty oil, for example, about 0.5-2.0% by weight. For this purpose, any good grade of animal or vegetable oil, such as lard oil, tallow oil, cottonseed oil, and the like, may be utilized. Good results have been obtained by adding about 1% of lard oil. It is essential that the fatty oil be added to the sulphurized mineral oil and not to the mineral oil before sulphurization, since the fatty substance is more easily sulphurized than mineral oil. Most of the sulphur is tightly bound in the fatty substance when a mixture of fatty substances and mineral oil is sulphurized. In order to obtain the best results, the fatty substance should be added at elevated temperatures, for example, about 340 to 380 F. When the mixture of fatty substance and sulphurized mineral oil has been stirred for five to fifteen minutes, it is found that the last trace of corrosiveness to copper previously retained by the sulphurized mineral oil will have been substantially completely removed.

When the mixture of fatty substance and sulphurized mineral oil has cooled to below 250 F., and preferably to about 180 to 200 F., lead naphthenate and the extreme pressure base, such as tricresyl phosphate, are added and blended thoroughly. It is desirable to add the lead naphthenate at as high a temperature as possible in order to obtain a homogeneous, stable product, but temperatures above 250 F. are generally to be avoided since the use of such elevated temperatures may result in the formation of sludge. The proportion of lead naphthenate should be about -20%, and preferably about 7.5%. The lead naphthenate inhibits corrosion and aids in the prevention of objectionable sludge formation.

The proportion of extreme pressure base is relatively small and is generally of the order of about 1 to 2%. For most purposes, 1% tricresyl phosphate is sulficient to impart desirable characteristics to the lubricant including high film strength. In addition to tricresyl phosphate, we may utilize other organic phosphates and phosphites, such as tricresyl phosphite, triphenyl phosphate, triphenyl phosphite, dibutyl phosphate, and dibutyl phosphite. Other suitable extreme bases may be employed, such as halogenated, especially chlorinated, aromatic or aliphatic compounds of the character of chlorinated diphenyl, chlorinated fats and fatty oils, and chlorinated wax. Other sulphurized aromatic extreme pressure bases, such as dibenzyl disulphide, may also be employed and provide a lubricant having desirable properties including high resistance to oxidation and thickening at elevated temperatures. However, there is a tendency for the lead naphthenate and the dibenzyl disulphide to react at temperatures of about 300 F. and over with the loss of the lead base and formation of lead sulphide sludge. Of the materials listed, tricresyl phosphate is preferred from the standpoint of efiectiveness, availability, and cost.

In order to further disclose the invention, the following example is given, it being understood that the example is merely for the purposes of illustration and the invention is not restricted thereto:

A lubricant was prepared utilizing the following constituents in the amounts specified:

The mineral oils used had the following characteristics:

Paraflin base 200 Pale residual oil Oil Gravity A. P. I 22.6 21. 3 Flash F. 575 360 Fire. .F 650 400 Viscosity at 210 F. seconds Saybolt Univers 190 Viscosity at 100 F. seconds Saybolt Universal 212 Four F 20 25 The blend of the heavy parafin base oil with the relatively light naphthene base distillate oil produces a very satisfactory stock for sulphurizing.

The mineral oil were blended in an ordinary grease kettle, and the sulphur was added while stirring. The batch was heated to about 400 F., and then maintained at 400 to 410 F. while stirring. At the end of about four hours of heating and agitating at 400 to 410 F., a sample was tested and found to be slightly corrosive to copper at 212 F. The mixture was then allowed to cool gradually to about 840 F., which required about two hours, and the lard oil was incorporated in the mixture at this temperature. A sample of the mixture at this stage was not corrosive to copper at 212 F. After cooling to about 200 F. the lead naphthenate was added with'thorough stirring. The tricresyl phosphate was then blended with the mixture, and the product was drawn off through a mesh screen to remove any suspended solids.

The product had the following characteristics:

Flash F 380 Fire F 440 Viscosity, seconds Saybolt Universal At F 62.4 At 210 F 101 Pour F 5 Corrosion:

Copper at 212 F. for 1 hour None Steel at 212 F. for 3 hours None Modified Indiana oxidation test (100 hours at Viscosity at 210 F. after 25 hours 115 Viscosity at 210 F. after 50 hours 131 Viscosity at 210 F. after 75 hours 157 Viscosity at 210 F. after 100 hours 180 Viscosity increase per cent 78 Timken test:

0. K pounds 35 Score do 40 The Viscosity increase of 78%, as determined according to the modified Indiana oxidation test, is much lower than the viscosity increase for gear lubricants now commercially available. For example, certain gear lubricants now commercially available give a viscosity increase of 2000% and more, when maintained at 300 F. for 100 hours in the modified Indiana oxidation test, and such excessive thickening renders the lubricants entirely unsuitable for high temperature operation. Moreover, in order to obtain high load-carrying capacity, it was necessary, in certain of the prior lubricants, to sulphurize under conditions which resulted in corrosive products. By the method of this invention, high load-carrying capacit is imparted to the lubricant and the corrosive properties are reduced to a minimum by the addition of such fatty substances as lard oil and such extreme pressure bases as tricresyl phosphate.

Obviously, many modifications and variations of the invention as heretofore disclosed may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

What we claim is:

1. An extreme pressure lubricant adapted for use in hypoid gears comprising essentially sulphurized mineral lubricating oil containing about 05-10% of active combined sulphur and about 0.5-2.0% of lard oil added at an elevated temperature following the sulphurization of the mineral oil, about 5.0-20.0% of lead naphthenate, and about 1.0-2.0% of tricresyl phosphate.

2. The lubricant of claim 1 in which the sulphurized mineral oil is prepared from a, blend of a heavy residual lubricating oil and a light distillate lubricating oil.

3. The process of preparing an extreme pressure lubricant which comprises sulphurizing mineral lubricating oil at a temperature of about 400 F.-425 F. with sufiicient sulphur to provide about 0.5-1.0% of active combined. sulphur in the 011, adding about 0.5-2.0% of a fatty substance at an elevated temperature after sulphurization of the mineral oil to render the sulphurized mineral oil non-corrosive to copper at 212 F., adding 5.0- 20.0% of lead naphthenate at a temperature below 250 F., and addingabout 1.0-2'.0% of an active extreme pressure base.

4. The process of preparing an extreme pressure lubricant which comprises heating a, mineral lubricating oil at about 400 F.-425 F. for a period of about four to eight hours with sufficient sulphur to incorporate about 0.5-1.0% sulphur in the mineral oil in an active combined form, adding about 0.5-2.0% of lard oil at about 340 to 380 F., adding about 5-20% of lead naphthenate at about 180 to 250 F., and adding about 1-2% of tricresyl phosphate.

5. A lubricant having extreme pressure characteristics consisting of a sulfurized mineral lubricating oil, about 0.52.0% of a fatty oil, about 5.0-20.0% of lead naphthenate, and about 1.0- 2.0% of an extreme pressure base containing an element of the group consisting of chlorine and phosphorus.

6. A lubricant having extreme pressure characteristics consisting of a sulfurized mineral lubricating oil, about 0.5-2.0% of afatty oil, about 5.0-20.'0% of lead naphthenate, and about 1.0- 2.0% of tricresyl phosphate.

'7. A non-corrosive extreme pressure lubricant consisting of a sulfurized mineral lubricating oil obtained by sulfurization at temperatures in the range of 400-425 F., about 0.5-2.0% of a fatty oil, about 5.0-20.0% of lead na'phthenate, and about 1.0-2.0% of an extreme pressure base selected from the group consisting of organic esters of phosphorus acids, halogenated aromatic and aliphatic hydrocarbons, halogenated fats and fatty oils, and sulfurized aromatic hydrocarbons.

8. A non-corrosive extreme pressure lubricant. consisting of a sulfurized mineral lubricating oil obtained by sulfurization at temperatures above 400 F. which is compounded with about 0.5-2.0% of a fatty oil, about 5.020.0% of lead naphthe nate, and about 1.0-2.0% of tricresyl phosphate. 9. A non-corrosive extreme pressure lubricant consisting of a sulfurized mineral oil obtained by sulfurization at temperatures of 400-425 F., compounded with a combination of about 0.5- 2.0% of lard oil, about 5.0-20.0% of lead naphthenate, and about 1.0-2.0% of tricresyl phosphate.

GUS KAUFMAN.

SAMUEL REGER PHILSON. 

